Power semiconductor devices such as Power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and IGBT (Insulated Gate Bipolar Transistor) have fast switching characteristics and reverse blocking voltage. Such devices are used widely for power conversion and control in electric appliances, communication devices, automobile motors, and other applications. Superjunction structures, which alternate p-type semiconductor regions and n-type semiconductor regions in an array within a semiconductor device have been receiving a lot of attention in order to increase efficiency and lower power consumption in these devices.
In these semiconductor chips, there are cases when superjunction structures are formed not only in the element region but also in the termination region outside of the element region. This is done to extend the depletion layer to the termination region when voltage is applied between the source and drain. With this kind of structure, the depletion region extends in to the element region and the termination region when OFF, which allows a high breakdown voltage to be maintained.
However, the high-voltage characteristic of superjunction structures presupposes that the charge quantities of each of the p-type semiconductor region and the n-type semiconductor region are properly balanced. Therefore, if each charge quantity fluctuates due to outside influence, its dependability (e.g., breakdown voltage) may be greatly reduced. For this reason, with a semiconductor chip equipped with a superjunction structure, it is necessary to sufficiently suppress the influence of charge from the outside in addition to properly preparing the charge quantity of the p-type semiconductor region and the n-type semiconductor region.
The problem that this invention tries to solve is to provide a semiconductor device with improved reliability.